docs: def _get_anelastic_attenuation_term(self, C, rrup):
          """
          Returns the anelastic attenuation term defined in equation 25
          """
          f_atn = np.zeros(len(rrup))
          idx = rrup >= 80.0
          f_atn[idx] = (C["c20"] + C["Dc20"]) * (rrup[idx] - 80.0)
          return f_atn